Process of separating hydrogen cyanide, ammonia, and carbon dioxide from gas mixtures containing them



Patented Nov. 16,

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PATENT err-16E 1 o rro mnexnnon'r, or .resiixronr-oicrnamam, GERMANY, assren'on. TO THE nonssnnn & nnssnncnna cnnrarcnn conrrm, on new" "roan, n. Y, a conronm TION- OF NEW YORK.

" rnocnssor snrana'rrne nxnnoenn' cramps, mmoma, AND cannon moxrnn anon eAs-mmrna-ns contrainrne rnnmt.

19' 7 from the. gas mixture first by means of sul r'uric acid, the ammonia present, then .sub-,

lioDrawingu "AppIication filed November 8, 1924, Serial No. 748,76fi, and in Germany November 26, 1923.

In certain manufacturing processes of producing hydrogen cyanide the gaseous hydrogen cyanide is obtained in association with ammonia,- carbon dioxide and, as the case'may be, one or inore other gases. The separation of the hydrogen cyanide from the gas mixture has hitherto caused great difiiculties and the results so far achieved, were very unsatisfactory.-

The procedure consisted in extracting .jecting the residual gas mixture containing carbon dioxide and the hydrogen cyanide, to a treatment with alcohol (comp. Germ. Pat. 104,953) or with water (comp. Ost. Lehrbuch der chemischen Technologie 11. edition page'184) whereby the hydrogen cyanide is withdrawn. The first method of using alcohol cannot be carried out on 9.

- large scale with success on account of economical reasons, whereas'the second process yields the hydrogen cyanlde in very dilute aqueous solutions only, which, in addition,

5 contain not inconsiderable quantities of carbon dioxide.

From these the. hydrocyanic acid has to be expelled bywarming, whereby the carbon dioxide is not wholly separated from the former, to be absorbed finally in alkali lye. This way of working necessitates a large plant and demands a considerable consumption of energy.

According to my present invention the problem of extracting the hydrogen cyanide from gaseous mixtures containing amongst other gases ammonia and carbon dioxide, is

1 solved in an excellent way by treating in a suitable manner the gaseous mixture with such salts of bases preferably of the alkaline earths including magnesium, the carbonates of which are less soluble in water than the salts used. If, for instance, the gaseous mixture is passed through a suspension of gypsum in water, a mixture is formed which contains calcium carbonate, ammonium.sulfate and, as the case may be, some gypsum not yet decomposed,'whereas thehydrogen cyanide, contrary to all expectations, passes.

through practically undecomposed. This could be the less anticipated as, on account of the calcium carbonate present, one had to reckon withthe decomposition or retention of considerable quantities of hydrogen.

' ture.

cyanide. Other salts,- also capable of form-' said salts to be used for thettreatment of the gaseous mixture, particularly such ammonium sulfate solutions 'for example whichhave been obtained by a previous treatment of such gaseous mixtures. In this way the ammonium sulfate is gradually concentrated in the solution.

If the ammonia and the carbon dioxide are present in the gas mixture to be treated inv a stoichiometric relation as regards ammonium carbonate, the hydrogen 1 cyanide escaping from the vessel, wherein the ammon1a and. the carbon dioxide have been absorbed, can be converted into alkali cyanide by absorption in caustic alkali solution without any further treatment. In the case of ammonia being present in excess of carbon dioxide it is advisable to make up the deficiency by adding carbon dioxide for example in the form of flue gases. Otherwise, the ammonia still present can be extracted subsequently from the escaping gaseous mixtreating the gas mixture in the well known way with sulfuric acid! An excess of carbon dioxide in proportion to the ammonia can be counter-balanced by the addition of the lacking quantity of ammonia, if the deficiency is relatively small. An excess of carbon dioxide, however, is not only not injurious to the process but may under cer-' tain conditions, even be advantageous. Such gases are theriifore worked up Without any preliminary treatment 'inaccordance with my present invention,the carbon dioxide coining 0E with the hydrogen cyanide being separated subsequently. This can be done by two methods; the first consists in adding to the caustic alkali solution intended for the absorption of the hydrogen cyanide such a quantity of lime as corresponds to the carbon dioxide still; present in. the gas mixture. Thereby, in addition to the readily solublealkali cyanide, sparingly soluble calcium carbonate is formed.

This can be done for instance by The second way. of obtaining a goodresultis the absorption of the gases by means of solutions which contain in addition to alkali metal sulfate or alkali metal carbonate, a

the suspension used for carrying through thequantity of slacked lime sufficient for the conversion of the alkali metal salts and for fixing the carbon dioxide present in the gases' An excess of'slacked lime is often very advantageous inthat the alkali metal sulphate or carbonate are then more completely transformed to the base and the gas absorption is consequently bettered. When a mixture of alkali sulfate and lime is used for the final absorption of hydrogen cyanide and its conversion into a cyanide of an alkali -forming metal the calcium sulfate formed by the reaction can be used for preparing main process of scrubbing the gaseous mixture containing'hydrogen cyanide, ammonia and carbon dioxide. The absorption of the hydrogen cyanide coming ofi the main i. e. the first stage of the process according to my invention can be carried through .by lime Water alone or by other bases offthesame group, with the provision that the conversion of the calcium cyanide formed is executed with alkali metalsalts whereby-insoluble or sparingly soluble alkaline earth salts are formed. Such salts are for example alkali metal sulfates or alkali metal carbonates. In those cases when the gas' mixture con- --tains carbon dioxide, in addition'itohydrogen. cyanide, the former is in the'co'urse of this process precipitated in the shape of in soluble calcium carbonate. of the calcium cyanide can be carried out in the way I have just been describing either in the presence of the calcium carbonate precipitate or after the separation ofvthe cyanide solution from the precipitate.

Whenthe gaseous mixture containing hydrogen cyanide, ammonia and carbon dioxide has passed the suspension for instanceof gypsum in water or the aqueous solution of another salt forming insoldble or dillicultly soluble carbonates the residual mixture consisting chiefly of ammonium sulfate v and, for instance, calcium carbonate, may

be made use of for the recovery of the ammonia. This may be achieved by heating the residual mixture, after the solution or suspension of the salts, the carbonates of which .are less soluble in water than the orig nal salts used, has been employed repeatedly or for a prolonged time and the contents of ammonium sulfate has been 111- creased as far as feasible. The gaseous mixture which escapes on heating is composed mainly. of ammonia and carbon dioxide. This mixture can advantageously be 1ntroduced into for instance the cyanizing process towhich nitrogenous organic materials for instance vinasse may be subjected in order to produce hydrogen cyanide. The

The conversion .monia and carbon dioxide with mower addition of ammonia has proved to be very.

beneficial, the yield of hydrogen cyanide being considerablyincreased thereby, whilst the presence of carbon dioxide which cs capes inassociation with the ammonia on heating the residues from V the absorption causes no injurious effect. After expelling the gases from the mixture as far as possible by heating the residue which consists of a. salt sparingly soluble in water, in the' example mentioned above for instance cal-- gen cyanide the separation of the hydrogen cyanide from a gas mixture comprising ammonia and carbon dioxide which consists in treatlng thegasmlxture wlthsalts of bases the carbonates of which are less soluble than the salts used, in the presence of water.

2. In a process of manufacturing hydro gen cyanide the separation of the hydrogen cyanide from agas mixture. comprising ammonia and carbon dioxide which consists in treating the gas mixture with salts of alkaline earths, the carbonates of which are less soluble than the salts used, in the presence of Water. I a

3. In a process of manufacturing hydrogen cyanide the separation of the hydrogen cyanide from a gas mixture comprising am-- monia and carbon dioxide which consists in treating the gas mixture comprising amgypsum in the presence of water.

4. In aprocess. of manufacturing hydrogen cyanide the separation of the hydrogen j cyanide from a gas mixture comprising am,- moina and carbon dioxlde which consists 1n treating the gas mixture with salts of bases,

the carbonates of which are less soluble than the'salts used, in the presence of Water, and

passing theescaping hydrogen cyanide into caustic alkali solution.

In a process of manufacturing hydro gen cyanide the separation of the hydrogen cyanide from a gas mixture comprising ammouia and carbon dioxide which consists in the carbonates of which are less soluble than the salts used, in the presence of water taking care that carbon dloxlde is present in treating the gas mixture with 'saltsof bases,

not" less than stoichiometric proportions withrcspoct to the ammonia present.

6. In a process of manufzmturing,hydrogen cyanide the separation of the hydrogen cyanide from a gas mixturecomprising ammonia and carbon dimcidewhich consists in treating the gas mixture with salts of bases the carbonates of which are less soluble than the salts used, in thepresence of water adding-carbon dioxide in the caseofits deficiency until it is present in not less than stoichiometric the ammonia;

7. 'In a process of manufacturing hydrogen cyanide the separation of the hydrogen cyanide from a gas mixture comprising a-mmonia and carbon dioxide which consists in treating the gas mixture with salts of bases.

the carbonates of which are less soluble than the salts used, in the presence of water adding more carbon dioxide than required toform ammonium carbonate 'with the ammonia present. I

8. In a process of manufacturing hydrogen cyanide the separation of the hydrogen cyanide from a gas mixture comprising ammonia and carbon dioxide which consists in treating the gas mixture with salts of bases the carbonates of which areless soluble than the salts used, in the presence of water adding flue gases in theplace of carbon dioxide.

9. In a process of manufacturing hydrogen cyanidefthe separation of the hydrogen cyanide from a gas mixture comprising ammonia and carbon dioxide which consists 1n treating the gas mixture with salts of bases the carbonates of'which are less sol'ublethjan v the salts used, in the presense o'fswater', add; ing more carbon dioxide than requiredto form ammonium carbonate with the, ammonia present, freeing the gaseous mixture from ammonia and converting the carbon dioxide into insoluble .calcium carbonate.

' 10. In a process of manufacturing hydrogen cyanide the separation of the hydrogen cyanide from thegaseous mixture comprismg ammonia and carbon dioxide, which consists in treating the gas mixture containing an excess of carbon dioxide over that required to form ammonium. carbonate with the ammonia present, with an aqueous suspension of gypsum, causing theescaping gas mix ture to react with alkali metal sulfate and lime in the presence of water and using the calcium sulfate thereby formed for the prep-- aration of fresh'suspensions for the absorption of ammonia and carbon dioxide from gaseous mixtures containing, in addition, hydrogen cyanide proportions with respect to Ina process of manufacturing hydro gen cyanide the separation of thehydrogen cyanide from the gaseous mixture comprisingammenia and carbon dioxide, which consists in treating the gas mixture with a suspension -of gypsum in ammonium sulfate solution. i

12. In a gen cyanide the separation of the hydrogen cyanide from the gaseous mixture comprise ing ammonia and carbon dioxide, which consists in treating the gas mixture having an excess of carbon dioxideover'that required to form ammonium carbonate'with the am-- monia present; with a'suspension of gypsum metal'sulfate and lime in the presence of water. f v

13. In a process of manufacturing hydrogen cyanide the separation of the hydrogen cyanide from the gaseous mixture comprissists in treating'the gas mixture having an excess of carbon dioxide over that required to form ammonium carbonate with the ammonia present,with a suspension of gypsum mg ammonia and carbon dioxide,,ivhich conprocess of manufacturing hydroin ammonium sulfate solution, causing theescaplng gas m xture to react with alkali in ammonium sulfate solution, causing the escaping 'gas'mixture to react with alkali metalsulfate and lime in the pres'enceof .water and using the calcium sulfate'thereby formed for the preparation of fresh suspensions for the absorption of ammonia and A. D. 1924. v

OTTO LIEBKNEGHT.

carbon dioxide from gaseous mixtures con- 

